Method and apparatus for multiple signal aggregation and reception in digital chaos network

ABSTRACT

The present invention teaches method and apparatus to transform a featureless, unpredictable, and non-repeatable chaos waveform into digital chaos waveforms that maintain featureless characteristics to serve as a for wireless communications protocol, whereby unintended observers cannot detect or disrupt yet imprint a small measure of predictability and repeatability to aid intend observers in recovering embedded information. This invention discloses wireless communication systems with multiple signal aggregation at the transmitter and multiple detection at the receiver that uses embedding digital signals and digital information within multiple digital chaos waveforms.

FEDERAL FUNDING LEGEND

This invention was produced in part using funds obtained through a grantfrom the Army Small Business Innovation Research. Consequently, thefederal government has certain rights in this invention.

FIELD OF INVENTION

This invention relates generally to wireless communication systems withmultiple signal aggregation at the transmitter and multiple detection atthe receiver. In particular, this invention relates to embedding digitalsignals and digital information within multiple digital chaos waveforms.

BACKGROUND OF INVENTION

A wireless communication device in a communication system communicatesdirectly or indirectly with other wireless communication devices. Fordirect/point-to-point communications, the participating wirelesscommunication devices tune their receivers and transmitters to the samechannel(s) and communicate over those channels. For indirect wirelesscommunications, each wireless communication device communicates directlywith an associated base station and/or access point via an assignedchannel.

Each wireless communication device participating in wirelesscommunications includes a built-in radio transceiver (i.e., transmitterand receiver) or is coupled to an associated radio transceiver.Typically, the transmitter includes at least one antenna fortransmitting radiofrequency (RF) signals, which are received by at leastone antenna of the receiver. When the receiver includes two or moreantennas, the receiver selects one of antennas to receive the incomingRF signals. Wireless communications between the transmitter with oneantenna and receiver with antenna is known as asingle-output-single-input (SISO) communications.

Well known communications systems provide a range extension on a SISOsystem by reducing the data rate and, as a result, increase the symbolduration and/or increasing transmit power. However, increasing transmitpower can lead to increase interference to other users sharing thenetwork. Therefore, what is needed is method for improved rangereception that does not lead to decreased network capacity or increasedsusceptibility to interference of the wireless device.

Generally speaking, transmission systems compliant with the IEEE 802.11aand 802.11g or “802.11a/g” as well as the 802.11n standards achievetheir high data transmission rates using Orthogonal Frequency DivisionModulation (OFDM) encoded symbols mapped up to a 64 quadrature amplitudemodulation (QAM) multi-carrier constellation. In a general sense, theuse of OFDM divides the overall system bandwidth into a number offrequency sub-bands or channels, with each frequency sub-band beingassociated with a respective sub-carrier upon which data may bemodulated. Thus, each frequency sub-band of the OFDM system may beviewed as an independent transmission channel within which to send data,thereby increasing the overall throughput or transmission rate of thecommunication system.

Similarly, multi-code spread spectrum system comprised of perfectlyorthogonal high-speed chaos spreading codes transporting independentmodulated data can be used to increase its overall throughput ortransmission rate of the SISO system. The high-speed “spreading signals”belong to the class of signals referred to as Pseudo Noise (PN) orpseudo-random signal. This class of signals possesses goodautocorrelation and cross-correlation properties such that different PNsequences are nearly orthogonal to one other. The autocorrelation andcross-correlation properties of these PN sequences allow the originalinformation bearing signal to be spread at the transmitter.

Transmitters used in the wireless communication systems that arecompliant with the aforementioned 802.11a/802.11g/802.11n standards aswell as other standards such as the 802.16a IEEE Standard, typicallyperform multi-carrier OFDM symbol encoding (which may include errorcorrection encoding and interleaving), convert the encoded symbols intothe time domain using Inverse Fast Fourier Transform (IFFT) techniques,and perform digital to analog conversion and conventional radiofrequency (RF) upconversion on the signals. These transmitters thentransmit the modulated and upconverted signals after appropriate poweramplification to one or more receivers, resulting in a relativelyhigh-speed time domain signal with a high peak-to-average ratio (PAR).

Transmitters used in direct sequence spread spectrum (DSSS) wirelesscommunication systems such as those compliant with commercialtelecommunication standards WCDMA and CDMA 2000 perform high-speedspreading of data bits after error correction, interleaving and prior tosymbol mapping. Thereafter, the digital signal is converted to analogform and frequency translated using conventional RF upconversionmethods. The combined signals for all DSSS signals are appropriatelypower amplified and transmitted to one or more receivers.

Likewise, the receivers used in the wireless communication systems thatare compliant with the aforementioned 802.11a/802.11g/802.11n and802.16a IEEE standards typically include an RF receiving unit thatperforms RF downconversion and filtering of the received signals (whichmay be performed in one or more stages), and a baseband processor unitthat processes the OFDM encoded symbols bearing the data of interest.The digital form of each OFDM symbol presented in the frequency domainis recovered after baseband downconverting, conventional analog todigital conversion and Fast Fourier Transformation of the received timedomain signal. Whereas receivers used for reception for DSSS mustde-spread the high signal after baseband downconverting to restore theoriginal information signal band but yields a processing gain equal tothe ratio the high speed signal to information bearing signal.Thereafter, the baseband processor performs demodulation and frequencydomain equalization (FEQ) to recover the transmitted symbols, and thesesymbols are then processed with an appropriate FEC decoder, e.g. aViterbi decoder, to estimate or determine the most likely identity ofthe transmitted symbol. The recovered and recognized stream of symbolsis then decoded, which may include deinterleaving and error correctionusing any of a number of known error correction techniques, to produce aset of recovered signals corresponding to the original signalstransmitted by the transmitter.

To further increase the number of signals which may be propagated in thecommunication system and/or to compensate for deleterious effectsassociated with the various propagation paths, and to thereby improvetransmission performance, it is known to use multiple transmission andreceive antennas within a wireless transmission system. Such a system iscommonly referred to as a multiple-input, multiple-output (MIMO)wireless transmission system and is specifically provided for within the802.11n IEEE Standard now being adopted and 3GPP-LTE Advanced and IEEE802.16m under development. As is known, the use of MIMO technologyproduces significant increases in spectral efficiency, throughput andlink reliability, and these benefits generally increase as the number oftransmission and receive antennas within the MIMO system increases.

In particular, in addition to the frequency channels created by the useof OFDM, a MIMO channel formed by the various transmissions and receiveantennas between a particular transmitter and a particular receiverincludes a number of independent spatial channels. As is known, awireless MIMO communication system can provide improved performance(e.g., increased transmission capacity) by utilizing the additionaldimensionalities created by these spatial channels for the transmissionof additional data. Of course, the spatial channels of a wideband MIMOsystem may experience different channel conditions (e.g., differentfading and multi-path effects) across the overall system bandwidth andmay therefore achieve different signal-to-noise ratio (SNRs) atdifferent frequencies (i.e., at the different OFDM frequency sub-bands)of the overall system bandwidth. Consequently, the number of informationbits per modulation symbol (i.e., the data rate) that may be transmittedusing the different frequency sub-bands of each spatial channel for aparticular level of performance may differ from frequency sub-band tofrequency sub-band. Whereas DSSS signal occupies the entire channelband, the number of information bits per modulation symbol (i.e., thedata rate) that may be transmitted using the different chaos sequencefor each spatial channel for a particular level of performance.

In the MIMO-OFDM communication system using a typical scheme, a highPeak-to-Average Power Ratio (PAPR) may be caused by the multiple carriermodulation. That is, because data are transmitted using multiplecarriers in the MIMO-OFDM scheme, the final OFDM signals have amplitudeobtained by summing up amplitudes of each carrier. The high PAPR resultswhen the carrier signal phases are added constructively (zero phasedifference) or destructively (±180 phase difference). Notably, OFDMsignals have a higher peak-to-average ratio (PAPR) often called apeak-to-average power ratio (PAPR) than single-carrier signals do. Thereason is that in the time domain, a multicarrier signal is the sum ofmany narrowband signals. At some time instances, this sum is large andat other times is small, which means that the peak value of the signalis substantially larger than the average value. Similarly, MIMO-DSSSschemes can have high PAPR for periodic sequence or binary-valuedsequence; however chaos spreading sequences do not exhibit either ofthese characteristics and therefore have better PAPR performance forSISO and MIMO operations.

The continually increasing reliance on SISO and especially MISO wirelessforms of communication creates reliability and privacy problems. Datashould be reliably transmitted from a transmitter to a receiver. Inparticular, the communication should be resistant to noise,interference, and possibly to interception by unintended parties.

In the last few years there has been a rapidly growing interest inultra-wide bandwidth (UWB) impulse radio (IR) communication systems.These systems make use of ultra-short duration pulses that yieldultra-wide bandwidth signals characterized by extremely low powerspectral densities. UWB-IR systems are particularly promising forshort-range wireless communications as they combine reduced complexitywith low power consumption, low probability of detection (LPD), immunityto multipath fading, and multi-user capabilities. Current UWB-IRcommunication systems employ pseudo-random noise (PN) coding forchannelization purposes and pulse-position modulation (PPM) for encodingthe binary information.

Others have proposed a periodic sequences of pulses in the context ofchaos-based communication system. Additional work has relied upon theself-synchronizing properties of two chaotic systems. In such a system,data is modulated into pulse trains using variable time delays and isdecodable by a coherent receiver having a chaotic generator matched tothe generator used in the transmitter. Such system is known in the artas a Chaotic Pulse Position Modulation (CPPM) scheme.

Such chaotic dynamical systems have been proposed to address the problemof communication privacy. Chaotic signals exhibit a broad continuousspectrum and have been studied in connection with spread-spectrumapplications. The irregular nature of a chaotic signal makes itdifficult to intercept and decode. In many instances a chaotic signalwill be indistinguishable from noise and interference to receivers nothaving knowledge of the chaotic signal used for transmission. In thecontext of UWB systems the use of non-periodic (chaotic) codes enhancesthe spread-spectrum characteristics of the system by removing thespectral features of the signal transmitted. This results in a lowerprobability of interception/detection (LPI/LPD) and possibly lessinterference towards other users. This makes the chaos-basedcommunication systems attractive.

There remains a need for improved chaotic coding/modulation methods toproduce such attractive communication systems. One prior art, U.S. Pat.No. 6,882,689, issued Apr. 15, 2005 to Maggio et al., attempts toimprove chaotic coding using pseudo-chaotic coding/modulation methodthat exploits the symbolic dynamics of a chaotic map at the transmitterto encode data. The method uses symbolic dynamics as “coarse-grained”description of the evolution of a dynamic system. The state space ispartitioned and a symbol is associated with each partition. The Maggioinvention uses a trajectory of the dynamic system and analyzes it as asymbolic system. A preferred transmitter of the Maggio prior art acceptsdigital data for coding and the digital data is allocated to symbolicstates according to a chaotic map using a shift register to approximatethe Bernoulli shift map acting as a convolution code with a number ofstates equal to the symbolic states defined on the chaotic map. Thepseudo-chaotically coded data is converted to analog form and modulatedinto synchronization frames in a transmitted signal.

The Maggio prior art has limitations in that it uses only one chaos map(e.g., Bernoulli shift map) that is generated based on the datatransmitted. By confining the mapping to Bernoulli shift, informationthat is repeated in each transmission or repeat symbol can be recognizedafter observing the waveform over an extended period of time. Oncecompromised, all future data will be detectable and decodable by ahostile system.

Another prior art system that teaches a chaotic coding/modulation methodis described in U.S. application Ser. No. 13/190,478, which is commonlyinvented by the present inventor, and incorporated herein by referencein its entirety. The system of the '478 application teaches a system,device and method for wirelessly transmitting data via a digital chaosspreading sequences. The '478 application system teaches constructingand storing a digital chaos spread code sequence in a volatile memory inboth the transmitter and the receiver. The system of the '478application eliminates the need to generate a digital chaos spread codesequence in the receiver. Information corresponding to the chaos spreadsequence used to transmit the digital information is received byreceiver for identifying which chaos spread code sequence to use toretrieve the coded information. The '478 application system furthereliminates the reliance on the Bernoulli shift map, and thereforeteaches a system which is less detectable by a hostile system.

While the system of the '478 application solves many of the problems inthe prior art, the system has limited applicability to SISO systems. Thereceiver disclosed in the '478 application detects and processes onedata stream for a single user even in the presence of other users orexternal interference. The '478 application therefore would not beuseful for transmission systems that jointly processes a plurality ofsignals detected at the receiver. For example, the joint processing ofmultiple signals allows for increased capacity and also enhancedreception of a MIMO system.

Generally, the most fundamental issue in wireless communication lies inhow efficiently and reliably data can be transmitted through a channel.The next generation multimedia mobile communication system, which hasbeen actively researched in recent years, requires a high speedcommunication system capable of processing and transmitting variousforms of information such as images and wireless data, different than aninitial communication system providing a voice-based service.

Then according to the prior art, what is needed is a system and methodthat does not sacrifice data rate in favor of range, provides increasedrobustness, while improving LPI/LPD, in a system detecting and receivingmultiple signals.

SUMMARY OF INVENTION

The present invention teaches improvements not found in the prior art.Specifically, the present invention teaches a system, device and methodfor wirelessly transmitting an aggregation of data via a multiplicity ofa digital chaos spreading sequence. In one aspect, the invention teachesthe use of plurality a priori constructed and stored digital chaosspreading code sequences for data aggregation of digital signals anddigital information within multiple digital chaos waveforms. In thecontext of this invention, data aggregation is any method or techniquewhereby several different data streams—whether for a single user ormultiple users—are collected or aggregated and processed together in asingle payload at a transmitter or receiver. Examples include, but notlimited, multiple chaos spreading sequences assigned to a single user toincrease their transmission rate through at least one transmit antenna;a cooperative network scheme whereby all users received within aspecified period of time are detected together, forwarded together(i.e., synchronized) as a single augmented payload through at least onetransmit antenna.

In another aspect of the invention a plurality of digital chaoswaveforms are chosen based on the intended application or operation. Forexample, a plurality of digital chaos waveforms may be chosen accordingto characteristics such as unity autocorrelation, very lowcross-correlation, and cyclostationary properties to low PAPR at thetransmitter and increased capacity by multiple simultaneous detection ofdigital signal and digital information with multiple digital chaoswaveforms.

In another aspect of the invention, a plurality of constructed digitalchaos spreading codes are stored in a volatile memory. The constructeddigital chaos spreading codes may be stored in the transmitter and inthe receiver.

In another aspect of the invention, with n a single group, the volatilememory may include distinct groups or memory locations for storing aconstructed digital chaos spreading sequence of a length N. The digitalchaos spread sequence may be partitioned into M number of groups ofequal number of even number of digital chaos spreading codesubsequences. Users are assigned a group ID from are stored in asequential order. The sequential ordering can be a known order, such asformal ordering of natural numbers (e.g., 1, 2, 3, . . . ). However, theordering does not need to be consecutive. The number is the index tosequences stored in at both the transmitter and receiver in a mannersuch as to provide a one-to-one correspondence between selected digitalchaos spreading code sequence at the transmitter and detected andrecovered index at the receiver.

In still another aspect, the invention discloses a data payloadincluding pre-ambles and mid-ambles, wherein the data payload may beaugmented for the inclusion of a signal field and a symbol delimiterwithin each of aggregated digital signals and digital information withinmultiple digital chaos waveforms so that the time of arrival of eachconstituent signal, part of the aggregated digital signals can beidentified accurately and reliably. A signal field detailing theoperational mode of the receiver containing at least one information oflength of the digital signal and digital information of the transmittingdata and rate of said. Further, a signal field comprised containingparity information for protection against and detection errors of otherinformation within the signal field.

In still another aspect, the invention teaches the uses of a transmittersystem with an augmented payload as described above.

In still another aspect, the invention teaches using a receiver systemwith an augmented payload.

In still another aspect, the invention teaches a system for transmittinga multitude of digital signal and digital information with multipledigital chaos waveforms.

In yet another aspect, the invention teaches a system for receiving amultitude of digital signal and digital information with multipledigital chaos waveforms.

In still another aspect, the invention teaches a receiver system capableof detecting each arrival times of the signal with the augmented payloadof multitude of digital signals and digital information with multipledigital chaos waveforms

In still another aspect, the invention teaches a receiver system capableof processing each signal field of the multitude of digital signal anddigital information with multiple digital chaos waveforms andconfiguring the remaining receiver subsystem to recover each of digitalsignal and digital information with multiple digital chaos waveforms.

In yet another aspect, the invention teaches a method for improvement ofmulti-user detection as described above, wherein the received multitudeof digital signals and digital information with multiple digital chaoswaveforms undergo a process to separate the aggregated transmitteddigital signal and digital information into streams projected on thenull space of the all users except itself. This partition is performedfor each of the identified digital signal and digital information partof the received aggregated transmitted digital signal and digitalinformation prior to processing by the dispreading subsystem.

In yet another aspect the invention teaches a method for aggregating andembedding multiple disparate communication signals within digital chaoscommunication waveforms originating from a multiple antennas. Theantenna elements of the multiple antenna system need not be co-locatedonly they work in cooperation for introducing low probability intercept(LPI) and low probability of detection (LPD), reduced peak-to-averageratio (PAPR), and increased network system capacity.

BRIEF DESCRIPTION OF DRAWINGS

A more complete understanding of the present invention may be derived byreferring to the various embodiments of the invention described in thedetailed descriptions and drawings and figures in which like numeralsdenote like elements, and in which:

FIG. 1 is an exemplary MIMO wireless transmission system that may beused with the various embodiments of the invention;

FIG. 2 is another exemplary MIMO wireless transmission system that maybe used with the various embodiments of the invention;

FIG. 3 is an exemplary wireless transmitter in accordance with variousembodiments of the invention;

FIG. 4 is an exemplary wireless receiver in accordance with variousembodiments of the invention;

FIG. 5 is a flowchart of an exemplary method for constructing of adigital chaos sequence according to various embodiments of the presentinvention;

FIG. 6 is an exemplary receiver synchronization process according tovarious embodiments of the invention;

FIG. 7 is an exemplary embodiment of packet formation according tovarious embodiments of the invention; and

FIG. 8 is an exemplary embodiment of null-space processor subsystem ofthe invention.

DETAILED DESCRIPTION

The brief description of exemplary embodiments of the invention hereinmakes reference to the accompanying drawing and flowchart, which showthe exemplary embodiment by way of illustration and its best mode. Whilethese exemplary embodiments are described in sufficient detail to enablethose skilled in the art to practice the invention, it should beunderstood that other embodiments may be realized and that logical andmechanical changes may be made without departing from the spirit andscope of the invention. Thus, the description herein is presented forpurposes of illustration only and not of limitation. For example, thesteps recited in any of the method or process descriptions may beexecuted in any order and are not limited to the order presented.

The present invention may be described herein in terms of functionalblock components and various processing steps. It should be appreciatedthat such functional blocks may be realized by any number of hardwareand/or software components configured to perform the specifiedfunctions. For example, the present invention may employ variousintegrated circuit (IC) components (e.g., memory elements, processingelements, logic elements, look-up tables, and the like), which may carryout a variety of functions under the control of one or moremicroprocessors or other control devices. Similarly, the softwareelements of the present invention may be implemented with anyprogramming or scripting language such as C, C++, java, COBOL,assembler, PERL, or the like, with the various algorithms beingimplemented with any combination of data structures, objects, processes,routines or other programming elements. Further, it should be noted thatthe present invention may employ any number of conventional techniquesfor data transmission, signaling, data processing, network control, andthe like. Still further, the invention could be used to detect orprevent security issues with a scripting language, such as JavaScript,VBScript or the like. For a basic introduction of cryptography, pleasereview a text written by Bruce Schneider which is entitled “AppliedCryptography: Protocols Algorithms, And Source Code In C,” published byjohn Wiley & Sons (second edition, 1996), which is hereby incorporatedby reference.

It should be appreciated that the particular implementations shown anddescribed herein are illustrative of the invention and its best mode andare not intended to otherwise limit the scope of the present inventionin any way. Indeed, for the sake of brevity; conventional wireless datatransmission, transmitter, receivers, modulators, base station, datatransmission concepts and other functional aspects of the systems (andcomponents of the individual operating components of the systems) maynot be described in detail herein. Furthermore, the connecting linesshown in the various figures contained herein are intended to representexemplary functional relationships and/or physical couplings between thevarious elements. It also should be noted that many alternative oradditional functional relationships or physical connections may bepresent in a practical electronic transaction or file transmissionsystem.

As will be appreciated by one of ordinary skill in the art, the presentinvention may be embodied as a method, a data processing system, adevice for data processing, and/or a computer program product.Accordingly, the present invention may take the form of an entirelysoftware embodiment, an entirely hardware embodiment, or an embodimentcombining aspects of both software and hardware. Furthermore, thepresent invention may take the form of a computer program product on acomputer-readable storage medium having computer-readable program codemeans embodied in the storage medium. Any suitable computer-readablestorage medium may be utilized, including hard disks, CD-ROM, opticalstorage devices, magnetic storage devices, and/or the like.

To simplify the description of the exemplary embodiment, the inventionis described as pertaining to a co-located MIMO DSSS system. However,the invention is applicable to distributive MIMO systems as well. Itwill be appreciated, that many applications of the present inventioncould be formulated. For example, the system could be used to facilitateany conventional wireless communication medium, and the like. Further,it should be appreciated that the network described herein may includeany system for exchanging data or transacting business, such as theInternet, an intranet, an extranet, WAN, WLAN, WPAN, HAN, Ad hocNetworks, mobile ad hoc networks (MANET), satellite communications(SATCOM), and/or the like.

FIG. 1 is an exemplary embodiment block diagram of a MIMO system 100useful for the invention. FIG. 1 shows a block diagram of an exemplarymultiple-input-multiple-output (MIMO) communication system 100,including a transmitter-receiver wireless channel 111 for transmitting amultiple wireless signals from a transmitter 102 to a receiver 104. Inan exemplary embodiment, transmitter 102 may have multiple antennas 218a-218 n. Similarly, receiver 104 may have multiple antennas 326 a-326 n.The exemplary MIMO communication system 100 may be implemented as partof a wireless local area network (LAN), wireless persona area network(PAN), wireless home area network (HAN) or metropolitan area network(MAN) system, a cellular telephone system, or another type of radio ormicrowave frequency system incorporating one-way or two-waycommunications over a range of distances. The exemplary MIMOcommunication system 100 and its sub-components will be described belowin more detail when required to facilitate the description of thepresent invention.

MIMO communication system 100 may employ various signal modulation anddemodulation techniques, such as single-carrier frequency domainequalization (SCFDE), direct sequence spread spectrum (DSSS) ororthogonal frequency division multiplexing (OFDM), for example. However,throughout this description, references will be made with respect to aMIMO communication system or a system including a transmitter andreceiver merely to facilitate the description of the invention. Further,in the interest of brevity, the description of communication system 100,may be described with respect to a wireless channel 111, although it isto be understood that the description related to wireless channel 111apply to each wireless MIMO channel 111. All the similar components ofthe wireless channels 111 will also have similar descriptions to eachother.

Transmitter 102 may transmit different signals from each antenna intransmit antenna array 218 a-218 n (transmitter antennas 218 a-218 n) sothat each signal is received by the corresponding antenna in thereceiving antenna array 326 a-326 n (receiving antennas 326 a-326 n).The signal is transmitted as an aggregate signal and received as anaggregation of all the transmit signals. All signals are transmittedonce and the receiver demodulates the aggregate signal. Themultiple-signal transmitter 102 may receive a data signal (i.e.,multiple data and/or other types of signals received) from a data source202 (information sequence 202) and split the data signal using asplitter 203. Splitter 203 splits the data signal into multiple signalsreceived by multiple-signal encoders 204 a-204 n. Signal encoders 204a-204 n may then encode the respective received signals from splitter203. The multiple signals from encoders 204 a-204 n may then bemodulated by respective chaos modulators 103 a-103 n. The signals fromchaos modulator 103 a-103 n may then be spatially mapped 207 andupconverted into distinct radio frequencies (RF) signals (RF1 205 a-RFn205 n) prior to being transmitted to the receiver 104 by respectivetransmitter antennas 218 a-218 n. Such signals may alternatively bereferred to alternatively as “an aggregate signal” “data,” “signals,”“information sequence,” and/or “data signals.”

The aggregate signal is received at the receiver 104 by receiver antennaarray 326 a-326 n and downconverted from the distinct RF signals (RF1207 a-RFn 207 n) prior to being combined by MIMO equalizer 211, whereinthe MIMO equalizer 211 is of traditional operation as is found in theart. The MIMO equalizer 211 equalizes the MIMO channel and recovers thetransmitted symbols received by all the receiver antennas (receiverantenna array 326 a-326 n) and transmits the symbols to respective chaosdemodulators 105 a-105 n. The chaos demodulators 105 a-105 n demodulatesthe received signals and sends the demodulated signals to respectivedecoders 320 a-320 n for decoding. The chaos demodulators 105 a-105 nreceives the respective signals and recovers the original signals thatwere provided by the data source 202. Once decoded, the separatelydecoded signals are merged by signal merger 209 prior to beingtransmitted to a data sink 107.

As depicted in FIG. 1, the original signals recovered by the decoders320 a-320 n are merged into a signal (merge 209) and may be transmittedto a connected data sink 107. Data sink 107 may include one or moredevices configured to utilize or process the recovered signals. As iswell known, receivers may additionally include other elements such assymbol mapper 318, symbol detection unit 316, Doppler Correction unit314, packet detection circuit 308, AD converters 304 and the like (shownin FIGS. 2-4) which are of the type which may be found in the prior art.

As previously noted, traditional MIMO WLAN transmission has problemsaddressed by the present invention. Namely, prior art systems such802.11x compliant system are more susceptible to interference, wirelesscollisions, and interception by unintended parties. The presentinvention addresses these problems by providing a system and method foraggregating and embedding multiple information-bearing communicationsignals within digital chaos communication waveforms occupying the samefrequency channel bandwidth transmitted with a multiple antenna system.By digital chaos what is meant is a waveform generated by sampling achaos signal, where chaos signals are determined by nonlinear dynamics:either stochastic or deterministic. Digital chaos sequences generatedaccording to the invention as described below, is used as a spreadingsequence in a transmitter 102 shown in FIG. 1.

With reference to FIG. 2, exemplary wireless MIMO transmitter 102includes a data source 202, stream splitter 203, spatial mapper 207, RFupconverters (RF 205 a-RFn 205 n), of similar operation as thecorresponding elements data source 202, splitter 203, spatial mapper207, and RF upconverters RF 205 a-RFn 205 n as in FIG. 1. Similarly,with reference to FIG. 2 wireless MIMO receiver 104 includesdownconverters (RF1 207 a-RFn 207 n), MIMO equalizer 211, stream merger209 and data sink 107 of similar description and operation as thecorresponding downconverters (RF1 207 a-RFn 207 n), MIMO equalizer 211,merger 209 and data sink 107 of FIG. 1.

With continued reference to FIG. 2, data source 202 is split intomultiple distinct signals by splitter 203. Splitter 203 splits thesignal into distinct signals and transmitted to respective symbolmappers 206 a-206 n. The symbol mapper 206 a-206 n may be a conventionalsymbol mapper including conventional transmitter components such as ascrambler, differential encoder, symbol generator or the like. Symbolmapper 206 a-206 n further transmits the respective signals to chaosspreader 213 a-213 n. Chaos spreader 213 a-213 n and symbol mapper 206a-206 b perform modulation of the respective data signals from streamsplitter with the digital chaos spreading code sequences as discussedmore fully below with respect to FIG. 5. The respective modulatedsignals are then spatially mapped (spatial mapper 207) and upconverted(RF1 205 a-RFn) prior to transmission to receiver 104, via therespective transmitter antennas via the transmitter antenna array intoMIMO channel (i.e., channel 111).

FIG. 2 receiver 104 receives the respective signals and downconverts thesignals (RF1 207 a-RFn 207 n). The downconverted signals are transmittedto MIMO equalizer 211. MIMO equalizer 211 equalizes the MIMO channel(i.e., channel 111) and recovers the transmitted symbols received by allthe receiver antennas (receiver antenna array 326 a-326 n) and transmitsthe symbols to respective chaos despreader 105 a-105 n. The respectivesignals from MIMO equalizer 211 are then demodulated using chaosdespreader 231 a-231 n and symbol demapper 318 a-318 n prior to beingmerged (stream merge 209) and provided to data sink 107.

With reference to FIG. 3, what is depicted is a detail description ofone of the exemplary multiple transmission streams of the MIMOtransmitter 102 of FIGS. 1 and 2. It should be understood that a similardescription of similar elements applies to any one of the transmissionsstreams noted above. In FIG. 3, transmitter 102 further includes a chaossequence memory 208, the operation of which is discussed with respect toFIG. 5. The chaos sequence memory 208 stores digital chaos sequences asdiscussed below.

The digital chaos sequences stored in chaos sequence memory 208 areconstructed according to the digital chaos sequence generation method ofFIG. 5. With reference to FIG. 5, digital chaos construction method 400,the digital chaos spreading code sequence is constructed by recordingnative analog chaos circuit or computer simulated non-linear dynamics ofdeterministic or stochastic mapping characteristics (Step 402). Therecorded segments are sampled such that successive samples appearindependent and segments of a predefined length and variable quantityhave low cross correlation (Step 404). Those samples may then be storedin memory (Step 406). Sampling rate can be varied or irregular, but thenumber of samples taken is fixed for a particular spreading factor andcan be any number (Step 408). Moreover, the period over which you samplecan be varied. In accordance with the invention, the segments arequantized (Step 410). The quantized recorded segments undergo theGram-Schmidt (GS) process (Step 412). The GS process on the sequenceensures that autocorrelation peak occurs at unity or near unity andcross-correlation between sequences is zero or nearly zero (e.g. m lowcross-correlation)—within the precision of the quantization process. Inone exemplary embodiment, the cross-correlation is less than −10 dB.

An Irregular sampling interval according to the invention may be, forexample, determined by modulo counting of known sequence generator suchas Fibonacci numbers, Lucas numbers, Perrin numbers or any pseudo randomnumber generators. For implementation ease with semiconductortechnologies for digital systems, the amplitudes may be quantized tofinite levels based on the maximum allowed cross-correlation (½^(L),where is L is the number of bits used to represent by each sampleamplitude) between code sequences. Independent segments or the digitalchaos sequences are grouped together to form a vector span fortransmitting the information-bearing communication signals or trainingsignals. The final step of the digital chaos process is to convert theindependent digital chaos segments into a group of orthonormal sequencesspanning the same subspace as the original segment. This process isperformed using the Gram-Schmidt orthogonalization procedure.

The memory may be partitioned such that groups of digital chaosspreading codes are stored independently of each other. For example, thedistinct groups may be organized according to the application for whichit will be used. Typical applications include any wireless applicationsrequiring voice over IP (VoIP) capability, video capability, and datacapability for point-to-point operation and/or point-to-multi-point.Inside the groups, the volatile memory is further partitioned into slotsfor storing a digital chaos sequence code. The slot is furtherpartitioned into a plurality of sub-slots for storing subsets of the ofthe digital chaos sequence.

Once the chaos sequence memory 208 is fully populated with digital chaosspreading sequences, the memory 208, the entire memory 208 is subjectedto Gram-Schmidt procedure, which converts the independent digital chaossegments into a group of orthonormal sequences spanning the samesubspace as the original segment. The memory requirement after theGram-Schmidt procedure is unchanged from those of the quantizedsegments. It is well-known in mathematics that any signal in ann-dimensional subspace can be unique represented an n scalar values thatcorresponds to the projection of the signal onto the orthonormal basesof the n-dimensional thus the need for Gram-Schmidt process in thisinvention method of apparatus

A preferred embodiment of the invention for the packet formation isshown in FIG. 7. In this exemplary embodiment the sample rate at thereceiver is targeted at 20 MHz and the chipping rate is proposed at 4Mcps at the transmitter. The minimum center frequency spacing betweenadjacent systems will be 5 MHz. The framing structure may be a radioframe of 10 ms divided into 5 sub-frames of equal duration 2milliseconds (ms) (600). These sub-frames may be configured as transmitor receive slot for any user.

A super-frame consists of several frames transmitted in succession with2 ms gap spacing between frames (610). Each frame to be transmittedconsists of a preamble training sequence, mid-amble training sequence,and data payload. The flexibility of frame structure can accommodate anumber of other embodiments catered to specific application. In thisembodiment, sufficient training information is included to detectsecurely and reliably. However, other embodiments might exists that makedifferent trades for different application requirements, For example,the length of the preamble, gap spacing between the frames or thewhether a mid-amble is included may depend on the application chosen.

As is well known, the key to a successful wireless design is toincorporate sufficient training information to recognize the arrival ofpackets, align symbol boundaries, estimate channel characteristic andcorrect for frequency offset. This embodiment utilizes a header fieldcomprises of a ten symbol preamble (602) and 48 symbol signal field(604) that defines the configuration state for the receiver. The dataportion of the frame varies from 0-200 symbols or 1-250 symbols (606)depending if it is the first frame of a super frame. The mid-amble, iftransmitted, consists of five additional training sequences in themiddle of the frame (608). All training sequences are modulated usingdifferential chaos shift keying (DCSK) and repeated a predeterminednumber of times; nine times and five times are shown for the preambleand mid-ambles, respectively, in FIG. 7. Each repetition is modulatedwith either a 1 or −1 according to normal DCSK techniques. Themodulation input can be an alternating sequence of positive and negativeones, which embeds with control information for the rest of the packet.The preamble and mid-ambles can have their powers significantly higherthat the data to aid in the synchronization at the receiver. Forexample, one embodiment used a 3 dB boosted in relative power to thedata samples. This will permit the high probability of detection withoutan overly burdensome overhead for the frame. If total overhead is 10% orless in duration for the frame, significant improvement in detection andsynchronization at the receiver is achievable for sacrificing only 0.79dB is signal power compared to no power boost. Each symbol is comprisedof a chaos sequence of predetermined length that can range from 16 chipsto 4000 chips, depending on the application requirements for throughputand covertness. The symbol delimiter field is a predetermined length. Anpreferred embodiment of the digital chaos used as twice that of thoseused to spread the data. One skilled in the art may choose a differentlength to meet other application or performance requirements. The signalfield is comprised on a 6 bit scrambling seed, which is used toinitialize the pseudorandom number (pn) generator for sequence patternand error check parity bits. The state of the registers of the pndetermines which of 2^(^6) stored sequence is selected or, optionally,which sequence in the chaos family should be transmitted for the currentsymbol.

With return reference to FIG. 3, transmitter 102 receives informationbearing signals 202 (i.e., information sequence 202). The format of datainformation of 202 may be bits, symbols, or sampled analog waveforms.The high speed chaos spreading sequence 208 multiplies the channel codedbits or symbol or directly the sampled analog waveform. The high speedchaos spreading transform the bit, symbol, or sample analog waveforminto a digital chaos waveform with information embedded in the amplitudeand phase of the digital chaos waveform compared to an exact replica 306at the receiver.

The signal transmitted by transmitter 102 is received by digital chaosreceiver 104 which recovers the embedded data. FIG. 4 is an exemplaryembodiment of a receiver 104 according to the present invention.Receiver 104 includes an antenna 326 a for receiving the transmittedsignal, channel filter 302 to reject signals not in the band ofinterest, analog-to-digital (A/D) converter 304 is used to sample andquantization the analog signal suitable for digital processing, chaosreplica repository 306 need for despreading, packet detection 308 todetermine when at least one packet arrives, matched filter 310 torecover symbol timing for at least one signal, channel estimate 312 toestimate and compensate the distortions to the waveform due to multipathfading, Doppler Correction 314 to estimate and correct frequency offsetsto due oscillator drift and mobility, symbol detect 316 to estimate themapping symbol sent by the transmitter, symbol D-map look-up table 318to recover informational symbol, Channel Decode 320 to recover theoriginal transmitted bits.

In recovering the data, receiver 104 receives the transmitted signal andrecovers the data signal by the following steps: The packets arecontinually searched until the receiver detects the arrival of a validpacket (502). The detection of the packet is based on the output of afree-running correlation (308) that exploits the preamble structure. Thevalidity of the packet is determined from the cyclic redundancy check(CRC) of the signal field (604). After the packet has been declaredvalid, the preamble is used to perform two synchronization processes:symbol timing estimation & correction (504) and frequency estimation &correction (506). A match filter or bank of matched filter (310) is usedto estimate the timing error and the appropriate correction is made inthe receiver timing. A separate correlator is used to estimate thefrequency errors (314) and the appropriate correction is applied to thebaseband received signal. The channel estimate is computed using thepre-computed convolution matrix based on the training symbols from thepreamble. The pseudo inverse of this matrix, which can be also computedoff-line since it doesn't change unless the preamble changes, is used tocompute the minimum mean square estimate of the channel taps (312)(508). Averaging is possible for each of process steps 502, 504, 506,and 508 based on the repetition of the training symbols in both thepreamble and mid-amble. The final processing step to process the payload(510), which consists of symbol detect (316), Symbol D-Map (318),Channel Decode (320), and finally, recovery of the information bits(322). It should be noted that there are two common receiver modes aspreferred embodiments. One, the high speed multiplication with Chaosreplica 306 occurs directly after the A/D. This embodiment is preferredwhen a sampled analog waveform is the information-bearing signal asshown in FIG. 2. Two, the high speed multiplication with Chaos replica306 occurs prior symbol detect 316 and after Doppler Correction 314 andChannel Estimation. This embodiment is best suited when theinformation-bearing signals are bits or symbols. Either configurationworks for the information-bearing signals in the form of bits or symbol,however configuration two has the best performance and configuration onehas the lower power consumptions. An improvement in the recovery of theinformation bits (322) is achievable if the data portion of theaggregated transmitted digital signal and digital information undergoesan addition process step prior to dispreading. This process steprequires separate digital streams to be constructed based on the nullspace of all signals except the one to be recovered. This process isrepeated for each signal declared valid by the check (CRC) of the signalfield (604).

FIG. 8 is an embodiment of an exemplary null-space processor subsystemwhich may be useful with this invention. In accordance with thisexemplary subsystem, the signal to be recovered (“the Selected i^(th)User Data”) and the remaining signals (the “Remaining User Data”) aremultiplied in the null space processor (Null Space for i^(th) SelectedUser corresponding to the Selected i^(th) User Data producing a signalcontaining the Remaining User Data signals. The Remaining User Datasignals are then subtracted from the signal containing the Selectedi^(th) User Data and the Remaining User Data such that Selected i^(th)User Data is output. In some instances, the output Selected i^(th) UserData may appear with residual signals from the Remaining User Data. TheSelected i^(th) User Data may then be recovered by using the Selectedi^(th) User Data to identify the i^(th) User Chaos Code for recoveringthe i^(th) User Data as described above with respect to FIG. 4.

It should be appreciated by one skilled in art, that the presentinvention may be utilized in any device that implements the DSSSencoding scheme. The foregoing description has been directed to specificembodiments of this invention. It will be apparent; however, that othervariations and modifications may be made to the described embodiments,with the attainment of some or all of their advantages. Therefore, it isthe object of the appended claims to cover all such variations andmodifications as come within the true spirit and scope of the invention.

We claim:
 1. A method of processing an aggregate data signal in wirelesstransmission, comprising: a. receiving an aggregate data signal at areceiving side, the aggregate data signal having a plurality of distinctdata signals containing distinct user data signals originating from aplurality of users, wherein each one of the plurality of distinct datasignals is modulated with a distinct chaos sequence at a transmittingside, and b. demodulating the each one of the plurality of distinct datasignal at the receiving side to extract the distinct user data signals,the modulating of the each one of the plurality of data signals beingperformed using a generated digital chaos sequence database containingthe distinct chaos sequence, wherein the generating of the distinctdigital chaos sequence comprises, recording a featureless waveformhaving nonlinear dynamics, sampling a fixed number of samples for aparticular spreading factor, storing a varied quantity of groups of thefixed number of samples for a particular spreading factor to form theentries of the database, such that the groups of fixed number of samplesfor a particular spreading factor are distinct with lowcross-correlation amongst the groups, and then processing all the groupssegments using Gram-Schmidt process.
 2. A method of claim 1, wherein thefeatureless waveform is one of at least one of a native analog chaoswaveform, a period waveform, computer simulated non-linear dynamics of adeterministic mapping characteristic, or stochastic mappingcharacteristic.
 3. The method of claim 1, each one of the plurality ofdistinct data signals includes control bits in a pre-amble and amid-amble of the plurality of distinct data signals.
 4. A method ofprocessing an aggregate data signal in wireless transmission,comprising: a. receiving an aggregate data signal at a receiving side,the aggregate data signal having a plurality of distinct data signalscontaining distinct user data signals originating from a plurality ofusers, wherein each one of the plurality of distinct data signals ismodulated with a distinct chaos sequence at a transmitting side, and b.demodulating the each one of the plurality of distinct data signal atthe receiving side to extract the distinct user data signals, themodulating of the each one of the plurality of data signals beingperformed using a generated digital chaos sequence database containingthe distinct chaos sequence, wherein the generating of the distinctdigital chaos sequence comprises, recording a featureless waveformhaving nonlinear dynamics, sampling a fixed number of samples for aparticular spreading factor to produce a group of independent digitalchaos segments, storing a varied quantities of digital chaos segmentsgroups and converting the group of independent digital chaos segmentsinto a group of orthonormal sequences spanning the same subspace as thegroup of independent digital chaos segments.